My experience with lithium batteries is extremely limited to those in our phones and laptops.
I've never tried using them as a build it project.
I have seen a Samsung phone go up in flames, be dosed with water, which made things even more interesting then knocked into a cooler filled with ice/water, which got way to interesting way too fast.
The lithium pulled oxygen from the water, leaving hydrogen which was all too happy to ignite and add to the fun. I think the only thing that 'contained' the fire was the lithium was all consumed and the ice kept things a bit cooler. Of course it did melt a hole in the bottom of the cooler.
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I have some primary lithium cells powered a remote project, solar powered on sunny days, switches to lithium at night, the lithium is protected by a zero loss diode I mentioned.
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I'd be tempted to place a constant current source in each light fixture and power the system with DC or a small PWM power supply in each fixture, again, powering with DC to avoid the complexities of a large PWM power supply.?
PWM and SMPS are tools of the devil. [both produce extreme EMI <radio noise> unless insane mitigation steps are taken. Insane to mean complex and expensive.
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We use self contained solar yard lights, they've been in service? about 3 years, all are working fine. I had to relocate 2 that weren't getting enough direct sunlight.
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I also have motion sensing AC mains powered lights. A friend teased me about being concerned about prowlers, I laughed, "Nope, don't want to break my neck by tripping over the !@#% mole hills in our yard."
[Do ya think I could buy a 500 feet of det cord and feed it into all their tunnels.....]
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